There are a number of different standards for data communication in networks. The most common form of network to which this invention relates is an Ethernet network. There are a number of communication standards which govern the speed at which data is transferred over such networks. Current Fast Ethernet networks operate at a theoretical maximum transmission speed of 100 Mbit/s. There are a number of standards for such communication, collectively known as 100BASE-T, such as 100BASE-TX (using two pairs of Cat 5 cable). Standards exist for transmission speeds of 10 Mbit/s to 1000 Mbit/s (1 Gbit/s) and above
The usual form of physical link is a copper wire-based infrastructure. When two devices are connected by a copper wire Ethernet network, and operate at different speeds (standards), there is an Ethernet procedure called ‘auto-negotiation’ which allows the two devices to choose common transmission parameters such as speed and duplex mode to allow them to communicate. Auto-negotiation resides in the physical layer of the OSI model and is currently covered by the international standard IEEE 802.3ab.
Auto-negotiation operates by connected devices detecting failure of a data communication link and then exchanging data relating to the technology abilities of each device. Upon receipt of this information, the devices decide on a mode of operation based on a priority list which forms part of the standard, currently spanning 10 Mbit/s to 1 Gbit/s.
The possibility of auto-negotiation on copper wire networks means that it is possible to progressively upgrade the capabilities of the various devices connected while still permitting full operation of the network. In this respect, the technology is backward compatible.
It is also possible to implement Ethernet networks using optical fibre links. These can also be configured to operate at different speeds. However, current standards covering such networks do not include anything comparable to auto-negotiation and so are not backward compatible. This invention is intended to address this problem.